The invention relates to a magnetic head for detecting a magnetic field representing information on a magnetic recording medium, said magnetic head having a head face and comprising a multilayer structure with at least one magnetoresistive layer of magnetic anisotropic material, said magnetoresistive layer having a central portion forming a magnetoresistive element and located between two end portions with a longitudinal axis directed from one end portion to the other end portion, said magnetoresistive element having an easy axis of magnetization extending at least substantially parallel to the longitudinal axis and being provided on one side with a layer comprising at least one equipotential strip which extends at an angle to the longitudinal axis.
A magnetic head of this type is known from U.S. Pat. No. 4,052,748 (herewith incorporated by reference).
The known magnetic head comprises an elongate magnetoresistive element of magnetic anisotropic material which has an easy axis of magnetization extending in the longitudinal direction of the element and a defined direction of magnetization extending at least substantially parallel to the easy axis of magnetization. Contacts for connecting the magnetoresistive element to a current or voltage source are provided at two end portions arranged opposite each other. The magnetoresistive element has satisfactorily conducting equipotential strips which are arranged at a minimum angle of 30.degree. and a maximum angle of 60.degree. with respect to the longitudinal axis of the magnetoresistive element. During operation the equipotential strips force an electric measuring current applied to the magnetoresistive element to flow through the element at an angle with respect to the easy axis of magnetization, while a longitudinal bias is generated. In practice, said angle of current flow is approximately 45.degree.. Under the influence of a magnetic field generated by recorded information of a record carrier moving along the magnetic head, the resistance of each part of the magnetoresistive element located between the equipotential strips decreases or increases, dependent on whether the direction of magnetization coincides with the current direction in the magnetoresistive element to a greater or lesser degree. In principal, a linear reproduction by means of a non-biased magnetoresistive head is possible. To improve the linearity of the behaviour of the magnetoresistive element, an auxiliary field may be applied.
It is known per se from U.S. Pat. No. 5,005,096 (herewith incorporated by reference) to provide in a thin film magnetic head hard-magnetic layers opposite end portions of a magnetoresistive layer, which layers are magnetostatically coupled to the magnetoresistive layer. A magnetoresistive sensor without equipotential strip or strips is arranged between said end portions. Instead of equipotential strips, the head has a soft-magnetic layer extending underneath and parallel to the magnetoresistive layer and separated therefrom by a non-magnetic layer. The soft-magnetic layer generates a transversal bias field in the magnetoresistive sensor for linearizing the sensor. Non-magnetic spacer layers of electrically conducting material, viz Cr, W, Nb or Ta are present between the hard-magnetic layers extending above the magnetoresistive layer and said end portions. The hard-magnetic layers also serve as electric conductors between electrically conducting connection tracks provided on the hard-magnetic layers and the electrically conducting spacer layers. Consequently, the connection tracks are electrically connected to the magnetoresistive layer via the hard-magnetic layers and the spacer layers.
A thin-film magnetic head of yet another type is known from U.S. Pat. No. 4,639,806 (herewith incorporated by reference), in which hard-magnetic thin layers are directly provided on end portions of a ferromagnetic thin film (MR element). The MR element is coupled in exchange with the hard-magnetic thin layers. The hard-magnetic thin layers are provided with electric conductors which are electrically connected to the MR element via the hard-magnetic thin layers.
It has been found that due to external influences such as, for example the presence of an external magnet or exposure to high temperatures, the adjusted direction of magnetization of the magnetoresistive element may be disturbed so that the operation of the magnetic head deteriorates. It has also been found that at small measuring currents the longitudinal bias due to the presence of equipotential strips is too low to prevent Barkhausen noise (spurious signals caused by the movement of magnetic domain walls in the magnetoresistive element).